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Discussion Starter #1
hi, yesterday my truck stop, couldn't start it, I have a brand new battery test the alternator and got 0 volts so I change the alternator and still no charging, I notice a little black box on the alternator could this part be my problem, how can I test it

thanks
 

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can you jump start it? your local auto parts should test them for free and recharge your bat...
 

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X2 ^^

And also take the alt and battery back and have both tested. You could have gotten bad ones. Check grounds.
 

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Discussion Starter #5
the truck start no problem, the thing is that I have no charging from the alternator, the 2 battery connectors are brand new like the battery and alternator
 

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the truck start no problem, the thing is that I have no charging from the alternator, the 2 battery connectors are brand new like the battery and alternator

Will the truck only start a few times before the battery dies? And also do the lights and dash look dim? If so then I would point my finger at the alternator.
 

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Do you have a sound system or anything that you have hooked up that needs power??
 

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Discussion Starter #8
alternator is new and was tested at the part's store, no radio in the truck, as the truck is running the voltage gets down slow, I can run for a couple of miles until the battery is dead
 

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When battery dies does truck die?
 

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Not sure about control box. You will have to wait on a XJ guy to tell ya that. But if it where my guess I would say bad alt.

I had the same thing happen to me with another car. And took the new alt back and had it tested. it was bad. So they gave me a new one. Tested it right there. tested great. So I put it on worked great for about a mile. Then same thing. Come to find out that alt went bad. (autozone) went to advanced and bought one tested it. No problems after that. Im not saying its who your buying it from. But it is possible to have a brand new alt go bad fast. They are not really brand new anyway. they are re-built. Thats why you have core charge on some things.
 

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sounds like a bad ground or a unwanted ground
 

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Okay, I'm not entirely sure with HO engines. But, I will tell you what I do know... RENIX alternators were internally regulated - I run the original 100A alt in my MJ, despite it being propane and having exactly zero factory wiring. However, a HO alt is externally regulated. Now, my thought is that it is regulated by the ECM. Yes. Only chrysler would be THAT stupid. So, when the ECM goes haywire and no longer regulates the alternator you have to buy a new ECM from chrysler (oh wait, not stupid, just trying to get your money). Some people realized that giving cash to chrysler for this reason was frankly a waste of cash. So, they install a $5 external regulator for some other model of vehicle. Typically it is a little black box that the alt plugs into. Now, I could be wrong about the alt regulator being in the ECM on an XJ - that might be on a Ram 2500.

If the alt passes, but it won't charge, and you'll need a new regulator. With a renix alt, when the regulator fails the alt comes back as a fail.
 

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Discussion Starter #14
I've done another test, if I put negative to one of the 2 little pole on the alternator, it start to charge but at 15.65V:confused:
 

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Discussion Starter #15
Okay, I'm not entirely sure with HO engines. But, I will tell you what I do know... RENIX alternators were internally regulated - I run the original 100A alt in my MJ, despite it being propane and having exactly zero factory wiring. However, a HO alt is externally regulated. Now, my thought is that it is regulated by the ECM. Yes. Only chrysler would be THAT stupid. So, when the ECM goes haywire and no longer regulates the alternator you have to buy a new ECM from chrysler (oh wait, not stupid, just trying to get your money). Some people realized that giving cash to chrysler for this reason was frankly a waste of cash. So, they install a $5 external regulator for some other model of vehicle. Typically it is a little black box that the alt plugs into. Now, I could be wrong about the alt regulator being in the ECM on an XJ - that might be on a Ram 2500.

If the alt passes, but it won't charge, and you'll need a new regulator. With a renix alt, when the regulator fails the alt comes back as a fail.
this is what I was affraid of:brickwall:

now I'm going to sleep and verify tomorow with another ECM, hope to find a good use one
 

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Man. im lost from here. Might have to wait for a XJ expert to shoot in here and say. "My XJ done that here is what I did." And 99.99% of the time you will have it fixed in no time.
 

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The calvary has arrived...

Your battery usually sits around 13.6 to 14V.

Getting a volt reading above 12V is normal, but 15V is getting borderline high, just make sure you're not boiling your battery.
So, this leads to one of two things, both being a bad Alt.

Sounds like almost bad diodes, and/or a bad regulator, which bad diodes could cause a Volt. Reg. failure...

If it's internally regulated, get a new Alt.,
If it's external, You might get away with changing the regulator and going on your merry way.

Start with that for now, I'll be able to give a little more info when I get home later and do a little research on what came with what...
 

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Good news (I had some free time at work):

Only the Renix Jeeps have external voltage regulators, which are controlled by the ECU, you have a post-Renix Jeep, so the regulator is in the Alt. itself.

Which means... New Alternator Time. Bring it in to check it, if possible, call them ahead of time to see if they can do a charging system test on the vehicle while it's running.
If not, just bring them the Alt. you just got and have them warranty out a new one. Then during the installation of the new one, double check for corrosion on all the terminals, snot them up with some dielectric grease, and make sure you have good connections...

:cheers:
 
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